A tracing control system uses a tracer head to detect amounts of displacement of respective axes applied to a stylus, and speed command values of the respective axes are calculated in a tracing calculating circuit by using these amounts of displacement. A cutter is moved relative to a workpiece by drive motors of the respective axes, in accordance with these speed command values, and at the same time, the tracer head is moved along the surface of a model at the same speed. This motion is repeated, and accordingly, the workpiece is machined to the same shape as the model.
Tracing control systems of this kind, however, have a problem in that regions of the model at which the shape is abruptly changed cannot be precisely traced. Namely, when the stylus comes to corners and the like of the model, an over-run of the tracer head occurs due to a delay in the reaction of the servo systems, or to the inertia of the machine or the like, and as a result, the overshot machining into the workpiece by the amount of over-run, and thus the machining precision at corners is lost.